A fuel cell is a device for directly converting the chemical energy of a fuel into electrical energy.
A fuel cell comprises two gas diffusion electrodes, an anode and a cathode, and an electrolyte impregnated matrix. The matrix is disposed between the two electrodes. A catalyst layer is disposed on the electrolyte-facing surface of each electrode. In the operation of a typical fuel cell, a hydrogen-containing gas is fed to the back surface of the anode and oxygen-containing gas is fed to the back surface of the cathode. The gases diffuse through the electrodes and react at the catalyst sites to yield electrical energy, heat and moisture.
On the anode side of the cell, hydrogen is electrochemically oxidized to give up electrons. The electrical current so generated is conducted from the anode through an external circuit to the cathode. On the cathode side of the cell, the electrons are electrochemically combined with the oxidant. A flow of ions through the electrolyte completes the circuit.
Several types of fuel cells have been developed and may be broadly categorized according to the type of electrolyte used. Acid-type cells using concentrated phosphoric acid as the electrolyte are the most commercially advanced to the various fuel cells.
Acid-type fuel cell power systems operate more efficiently and with increased power density in a pressurized environment. In a pressurized fuel cell power plant the fuel cell stack is enclosed in a containment vessel. Pressurized reactant streams i.e. fuel and oxidant are supplied to the fuel cell stack. The containment vessel is maintained in an elevated pressure to reduce the driving force for hydrogen leakage from the fuel cell stack. Typically, nitrogen is employed as the inert gas stream. The storage of nitrogen as a high pressure gas or as a cryogenic liquid is cumbersome. Alternatively, an inert exhaust gas may be provided by the combustion of a fuel in air. These conventional methods for providing an inert gas stream have proven to be costly and cumbersome.